Ultrasonic Cleaning in Dentistry

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ultrasonic cleaning of dental instruments

Cleanliness. If there’s one word that dominates the lives of almost every medical professional, it’s cleanliness. Everything in a dentists’s office must be clean on a patient by patient basis. Surfaces need to be wiped down, paper changed, and most importantly, instruments must be sterilized.

The risk of spreading infection during oral medical procedures is by it’s very nature extremely high, do to how delicate tissues in the mouth can be. This is why ultrasonic cleaners are so popular in the medical field. No other cleaning method cleans is quickly, or as thuroughly, especially in large batches.

How Does Ultrasonic Cleaning Work?

Ultrasonic baths take advantage of a phenominon known as “cavitation”. Through this process, high frequency sound waves are used to create microscopic vacuum bubbles, that when forced against the object being disenfected, collapse, forcing the surrounding cleaning solution to fire into the space it once occupied.

This creates a powerful “scrubbing” action that gets into even the tiniest spaces. As you can imagine, this is a huge advantage when cleaning dental instruments.

Choosing an Ultrasonic Instrument Cleaner & Solution

When choosing the cleaner that is right for your specific facility, there are two major factors to consider.

The first is the size of the instruments you are cleaning, and the second is how many of those instruments do you want to clean at once. These two factors will determine the size of tank you need, along with your cleaning cycle time.

Many units also give you the choice of heat or no heat, and analog or digital controls. We suggest a heated, digitally controlled unit, such as the CPX3800H. Heat is very important for cleaning and disinfecting, and also assists in ultrasonic transmision. Digital controls have the advantage of batch to batch consistency, and precise power and temperature control.

What kind of solution goes into the tank? The solution you use will depend on whether you are focused on cleaning, decontamination, or both.

If you just want to clean, Branson MC-3 will do the job. It is biodegrable, aluminum safe and an emulsifier – meaning that it will hold particulate in suspension, preventing re-deposition onto your instruments.

If you need to disinfect as well, take a look at something like Micricide:

  • EPA registered to kill Hepatitis B and HIV (AIDS) virus
  • OSHA compliant with bloodbourne pathogens standard as stated in 24 CFR 1910

Cleaning and Disinfecting Dental Instruments

The actual cleaning of dental instruments and similar items in an ultrasonic washer is a fairly simple afair:

  1. The number one thing on your to-do list for this process is to have a test for clean. Without an objective standard for cleanliness, how can you tell if the job is done? Since we are concerned mainly with removing organic debris, this can be as simple as the following: “When observed under 20x magnification, the instruments have no detectable soil remaining.” If you check your facility’s regulations, you will most likely find that this spec already exists.
  2. Briefly rinse the instruments. While your cleaner will remove even the most tenacious soils, there is no reason to contaminate your cleaning solution with easily rinsed off debris.
  3. Fill the tank to the indicated “fill line” with clean water and disinfectant / cleaning soluion. Temperature should be set to 150-160 degrees farenheit. If your tank has a simple ON/OFF heating function, this is where it is most likely set. Manual Branson tabletop units for example will heat up to about 156F. If you can adjust the heat, set it to about 80% of the maximum. Remember that while ultrasonic cleaning will remove soils, it does not on its own disinfect completely. You may need to add a disinfecting agent to the tank, or even use an autoclave. Check your organization’s requirements for instrument cleaning to be sure you comply.
  4. Run the tank for five to ten minutes with nothing in the tank but your solution. This will assist the heater in reaching the desired temperature, and will also “de-gas” the solution. De-gassing is a process whereby trapped air in your cleaning solution is driven out by ultrasonic activity. This is necessary because until this gas is cleared, some of the energy will be wasted on this instead of being used for cleaning. This can throw off your results, and give you an incorrect indication of the required cleaning time.
  5. Lower instruments, or racks of instruments, into the tank. You will need to use a basket or a support rack. You cannot set parts on the bottom of an ultrasonic tank, as that is where the transducers are located. In anyevent, using a basket makes getting clean (and hot!) parts a lot easier to get out of the tank. Set temperature, power, and cleaning time to desired perameters. Start with 3 minutes at 155F and see where that leaves you. If you still do not meet requirements, increase the cycle time and / or temperature. Note that after 20 minutes, little additional cleaning will take place.
  6. Record your results! Always strive to develop the cleaning process that takes the least time, heat and cleaning solution concentration. This will make your process as effective and economical as it can be while still meeting spec. Some experimentation is in order.
  7. At the end of the cycle, remove instruments from tank, dry with high temperature filtered compressed air if available. Air drying is fine as well.

Beyond Instrument Cleaning

Ultrasonic cleaners are also very popular for cleaning other dental related items, especially for consumers. Some examples of commonly cleaned dental items include:

Dentures – Many people have discovered the ease and effectiveness of cleaning their dentures in an ultrasonic bath. Since ultrasonic cleaning is so precise, all odor causing bacteria is stripped away with each cleaning, leaving dentures clean and fresh.

Retainers – Just like dentures, retainers can become soiled and odorous in short order. With the proper cleaning solution, retainers can be cleaned to a like new condition.

Does ultrasonics work for dental instruments?

Yes! Aside from the anecdotal evidence provided by thousands of dental offices and hospitals, many studies have been done indicating that ultrasonic cleaning is an effective method not only for removing organic cantaminants, but reducing viral load:

Effectiveness of ultrasonic cleaning of dental instruments

Cafruny WA1, Brunick A, Nelson DM, Nelson RF.

PURPOSE: To quantitate blood contamination present on dental instruments used for routine prophylaxis and to assess the effectiveness of ultrasonic decontamination in reducing blood and virus contamination on dental instruments.

MATERIALS AND METHODS: Human blood contamination present on dental instruments obtained after routine prophylaxis was analyzed using IgG as a blood marker. RESULTS: The estimated contaminating blood volume was found to normally range between 1.4 x 10(-6) to 2.0 x 10(-4) ml.

Attempts to saturate the instruments with blood contamination suggested that the maximum possible retained blood volume was about 10-fold higher than the normal levels of contamination. Hand scrubbing of contaminated instruments was both relatively ineffective and inconsistent in removing blood contamination.

Decontamination in an ultrasonic cleaner was more effective than hand washing, resulting in greater than a 100-fold reduction of blood contamination. Using a mouse model virus (lactate dehydrogenase-elevating virus, LDV), high levels of virus contamination of dental instruments and dental handpieces were achieved, as determined by assay of residual virus.

Ultrasonic treatment reduced the level of virus contamination present on dental instruments by one million-fold, and virus contamination present in dental handpieces was reduced by one thousand-fold.

These results provide quantitative estimations of the infection threat and its reduction by ultrasonication, posed by human-exposed dental instruments.

The value of ultrasonic cleaners in dental practice

Bentley EM.

Ultrasonic cleaners are a valued aid to instrument cleaning in many general dental practices. This article reviews the different ways their cleaning efficiency has been assessed. It is recommended that burs and files should be cleaned ultrasonically before first use.

Prophylaxis cups are not sufficiently decontaminated by ultrasonic cleaning and therefore should be discarded after use. Although instruments are visibly clean after ultrasonic cleaning and generally clean when viewed with an electron microscope, ultrasound alone is insufficient for sterilisation. Further avenues of research have been highlighted.

PMID: 8060709 [PubMed – indexed for MEDLINE]

Evaluation of biological debris on endodontic instruments after cleaning and sterilization procedures

Popovic J1, Gasic J, Zivkovic S, Petrovic A, Radicevic G.

AIM: To examine the presence of biological debris and the level of contamination on reusable endodontic instruments those were subjected to different cleaning methods prior to sterilization.

METHODOLOGY: One hundred and eighty endodontic instruments from eighteen dental practices were analysed. These practices used different decontamination protocols for reusable instruments. The presence of organic debris was detected by the use of Van Gieson’s stain. Forty-eight new stainless steel hand instruments were used as controls. The samples were examined by light microscopy.

RESULTS: Residual biological debris was observed in 96% of the samples. The mean value of maximum biological contamination was 34% in the group in which the instruments were brushed manually and immersed in alcohol, 25% in the group in which commercially available disinfectants were used and 5% in the group in which the instruments were cleaned ultrasonically.

There was a statistically significant difference in the mean values with respect to the cleaning protocol applied (P < 0.001). CONCLUSIONS: The methods used to clean endodontic instruments appear to be generally ineffective for the removal of biological debris. The best method was the one that included mechanical, chemical and ultrasonic cleaning of instruments. PMID: 20487454 [PubMed – indexed for MEDLINE]

Comparison of an ultrasonic cleaner and a washer disinfector in the cleaning of endodontic files

Perakaki K1, Mellor AC, Qualtrough AJ.

The aim of this study was to compare the amount of residual organic debris on endodontic instruments that had been cleaned in either an ultrasonic bath or a washer disinfector prior to sterilisation. A total of 90 endodontic files of varying sizes were used to clean and shape root canals in extracted teeth and were then placed in endodontic file holders.

Test group 1 (36 files) were ultrasonically cleaned for 10 min and test group 2 (36 files) were cleaned in a washer disinfector. A control group (18 files) were not cleaned at all. Following sterilisation, all the files were visually inspected under a light microscope and scored using an established scale.

The results showed that both test groups had significantly less residual debris than the control group.

Comparing the test groups, the files that had been cleaned ultrasonically had significantly less debris than those cleaned in the washer disinfector.

The design of the instrument holder may have been a factor in this result. More research is needed into the use of washer disinfectors in the cleaning of small dental instruments that have a complex surface structure.

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  • David Huckabay
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